Field of the Invention
The present invention is directed to a hybrid spring device comprising an outer tubular shell and an inner part enclosed in the outer tubular shell comprising a fibre reinforced plastic material which is in particular useful for automotive applications. The invention is further directed to methods for producing a hybrid spring device of this kind.
Discussion of Related Art
Spring devices for automotive applications such as axle springs or torsion bars must show a defined deformation characteristic in an environment where they are exposed to strange chemical and physical impacts.
The spring devices currently used are mainly made from metallic materials. To improve their properties in particular against corrosion they are subjected to various treatments including heat treatments. Surface coatings using epoxy resins are common as well. Though such treatments are effective in protecting the metallic spring devices against corrosion, their deformation characteristic is almost exclusively governed by the properties of the metallic material, this limiting the optimization of the spring characteristics.
The prior art on the other hand teaches spring devices for automotive applications made from fiber reinforced plastic materials.
For example, W012035239 discloses a suspension spring for a motor vehicle made from a composite material including fibres and resin, wherein the composite material forms the outer layer of the spring. Use of carbon fibres is mentioned.
FR2837250 discloses a helical spring that may be used as an axle spring. The helically wound spring wire has a core part and an outer layer both made of fibre reinforced composite material. The central part is a first wire comprising elongated fibres extending unidirectional along the axis thereof. The outer layer is made of a ribbon or a second wire comprising elongated fibres extending unidirectional along the axis thereof, too. For forming the outer layer the ribbon or second wire is wrapped around the first wire at an angle relative to the axis of the first wire.
WO02099307 discloses a fibre-reinforced composite spring comprising a coiled spring wire that comprises a fibre-reinforced core having a longitudinal axis, where the core comprises core-reinforcing fibre tows that are twisted about the longitudinal axis of the core. An outer layer surrounding the fibre-reinforced core comprises a resin that is devoid of fibre tows.